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Sprinkler actuation time has been calculated for various cases, but there has been little study on extinguishing time after sprinkler actuation. Therefore, we have tried to draw an equation for the prediction of extinguishing time in the compartment fires where the ceiling is not high, and burning rate and water discharge rate are comparatively low. It is considered that the fire extinguishing performance depends on the interaction of sprinkler sprays with buoyant plumes, and cooling effect on a fire source by water discharge. The ratio of the updraft gas velocity in the plume to the velocity of water drops is considered as the former factor, and the ratio of the burning rate to the water discharge rate as the latter. We have obtained a generalized equation for the extinguishing time after sprinkler actuation by dimensional analysis, using these factors. We also attempted numerical calculation of extinguishing time for an example by this equation. This is the case of a crib fire with a constant burning rate. We consider that the extinguishing time for sprinklers will become one of the important factors on extinguishing performance of sprinklers.